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Encyclopedia > VESA Local Bus
SVGA VLB card
VLB and ISA slots on a motherboard
VLB and ISA slots on a motherboard

The VESA Local Bus (usually abbreviated to VL-Bus or VLB) was mostly used in personal computers. VESA Local Bus worked alongside the ISA bus; it acted as a high-speed conduit for memory-mapped I/O and DMA, while the ISA bus handled interrupts and port-mapped I/O. Image File history File links VLB SVGA card. ... Image File history File links VLB SVGA card. ... Super Video Graphics Array, almost always abbreviated to Super VGA or just SVGA is a broad term that covers a wide range of computer display standards. ... Image File history File links VLB slots on a motherboard. ... Image File history File links VLB slots on a motherboard. ... This article or section does not adequately cite its references or sources. ... A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... The Video Electronics Standards Association (VESA) is an international body, founded in the late 1980s by NEC Home Electronics and eight other video display adapter manufacturers. ... This article or section does not adequately cite its references or sources. ... Memory-mapped I/O (MMIO) and port I/O (also called port-mapped I/O or PMIO) are two complementary methods of performing input/output between the CPU and I/O devices in a computer. ... Direct memory access (DMA) is a feature of modern computers, that allows certain hardware subsystems within the computer to access system memory for reading and/or writing independently of the central processing unit. ... Memory-mapped I/O (MMIO) and port I/O (also called port-mapped I/O or PMIO) are two complementary methods of performing input/output between the CPU and I/O devices in a computer. ...


A VLB slot itself was an extension of an existing ISA slot. Indeed, both VLB and ISA cards could be plugged into a VLB slot (although not at the same time.) The extended portion was usually coloured a distinctive brown. This made VLB cards quite long, reminiscent of the expansion cards from the old XT days. The addition resembled a PCI slot. The IBM Personal Computer XT (IBM 5160), often shortened to the PC XT or simply XT, was IBMs successor to the original IBM PC. It was released on March 8, 1983, and was one of the first computers to come standard with a hard drive. ...


The VESA Local Bus was designed as a stopgap solution to the problem of the ISA bus's limited bandwidth. VLB had several flaws that served to limit its useful life substantially: This article or section does not cite its references or sources. ...

  • 80486 dependence. The VESA Local Bus relied heavily on the 80486's memory bus design. When the Pentium processor started to gain mass acceptance, circa 1995, there were major differences in its bus design, and the VESA Local Bus was not easily adaptable. This also made moving the bus to non-x86 architectures nearly impossible. Few Pentium motherboards with VLB slots were ever made. IBM offered an OPAL motherboard based on the IBM 486SLC2 CPU with two VLB slots.
  • Limited number of slots available. Most PCs that used VESA Local Bus had only one or two slots available, as opposed to 5 or 6 ISA slots. This was because, as a direct branch of the 80486 memory bus, the VESA Local Bus did not have the electrical ability to drive more than 1 or 2 (or 3 at the most) cards at a time.
  • Reliability problems. The same electrical problems that limited the VESA Local Bus to 2 or 3 slots also limited its reliability. Glitches between cards were common, especially on low-end motherboards, and when important devices such as hard disk controllers were attached to the bus, there was the all-too-common possibility of massive data corruption.
  • Installation woes. The length of the slot and number of pins made VLB cards notoriously difficult to install and remove. The sheer mechanical effort required was stressful to both the card and the motherboard, and breakages were not uncommon. This was compounded by the extended length of the card logic board; often there was not enough room in the PC case to angle the card into the slot, requiring it to be pushed with great force straight down into the slot.

Despite these problems, the VESA Local Bus was very commonplace on 486 motherboards. Probably a majority of 486-based systems had a VESA Local Bus video card, although early 486 systems never had VLB slots, as VLB debuted years after the introduction of the 486 processor. The Pentium is a fifth-generation x86 architecture microprocessor from Intel. ... 1995 (MCMXCV) was a common year starting on Sunday of the Gregorian calendar. ... An Intel Pentium 4 chip; early Northwood build x86 or 80x86 is the generic name of a microprocessor architecture, first developed and manufactured by Intel. ... International Business Machines Corporation (known as IBM or Big Blue; NYSE: IBM) is a multinational computer technology and consulting corporation headquartered in Armonk, New York, USA. The company is one of the few information technology companies with a continuous history dating back to the 19th century. ... A motherboard is the central or primary circuit board making up a complex electronic system, such as a modern computer. ... Typical hard drives of the mid-1990s. ... Data corruption refers to computer data that when transmitted, arrives at its destination as different than when it was transmitted from the source. ...


By 1996, the Pentium (driven by Intel's Triton chipset and PCI architecture) had eliminated the 80486 market, and the VESA Local Bus with it. Many of the last 80486 motherboards made have PCI slots in addition to (or completely replacing) the VLB slots. 1996 (MCMXCVI) was a leap year starting on Monday of the Gregorian calendar, and was designated the International Year for the Eradication of Poverty. ... This is a list of computer motherboard chipsets made by Intel. ... This article or section does not cite its references or sources. ...


Technical data

Bus width 32 bits
Compatible with VLB
Pins 112
Vcc +5V
Clock 486SX-25: 25 MHz
486DX2-50: 25 MHz
486DX-33: 33 MHz
486DX2-66: 33 MHz
486DX4-100: 33 MHz
486DX-40: 40 MHz
486DX2-80: 40 MHz
486DX4-120: 40 MHz
486DX-50: 50 MHz (out of specification)

Image File history File links Download high resolution version (756x1513, 62 KB) Source / Photographer: Appaloosa 19:44, 14 November 2005 (UTC) File links The following pages link to this file: VESA Local Bus ... PIN can mean different things: Personal identification number Postal Index Number Personal Internet Name. ... VCC is an abbreviation for common-collector voltage. It most likely originated as the supply voltage for a common collector amplifier. ...

Humor

The acronym VLB was sometimes alternatively expanded to Very Long Bus because of the length of the slot and the cards that fit in it. It has been suggested that this article or section be merged with Backronym and Apronym (Discuss) Acronyms and initialisms are abbreviations, such as NATO, laser, and ABC, written as the initial letter or letters of words, and pronounced on the basis of this abbreviated written form. ...


See also


This article is part of a series on computer expansion buses. This article or section does not adequately cite its references or sources. ... Three EISA Slots. ... This article or section does not adequately cite its references or sources. ... NuBus is a 32-bit parallel computer bus, originally developed at MIT as a part of the NuMachine workstation project, and eventually used by Apple Computer and NeXT Computer. ... This article or section does not cite its references or sources. ... This article or section does not adequately cite its references or sources. ... PCI Express (formerly known as 3GIO for 3rd Generation I/O, not to be mistaken with PCI-X) is an implementation of the PCI computer bus that uses existing PCI programming concepts and communications standards, but bases it on a much faster serial communications system. ... This is a list of device bandwidths: the channel capacity (or, more informally, bandwidth) of some computer devices employing methods of data transport is listed by bit/s, kilobit/s (kbit/s), megabit/s (Mbit/s), or gigabit/s (Gbit/s) as appropriate and also MB/s or megabytes per...

Preceding: ISA
Subsequent: PCI


This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL. Image File history File links Steps. ... This article or section does not adequately cite its references or sources. ... This article or section does not cite its references or sources. ... The Free On-line Dictionary of Computing (FOLDOC) is an online, searchable encyclopedic dictionary of computing subjects. ... GNU logo (similar in appearance to a gnu) The GNU Free Documentation License (GNU FDL or simply GFDL) is a copyleft license for free content, designed by the Free Software Foundation (FSF) for the GNU project. ...


  Results from FactBites:
 
VESA Card Size, VESA PinOut, VESA Local Bus, VLB (474 words)
The VLB was released in 1992 and operated as a PC Local Bus Expansion.
However, VESA Local Bus board may be found in legacy equipment.
The PCAT bus [ISA] was an up-grade to the original PCXT bus, and the VLB bus was an up-grade to the PC-AT bus.
Please title this page. (Page 3) (589 words)
The first VESA devices were video controllers, and they were placed on a VESA A local bus which was connected directly to the host CPU bus.
The interface between the CPU bus and the VESA A bus must be CPU dependent - the controller that communicates between the CPU and the host bus speaks only to the particular family of CPUs it was designed for (486, 386, etc.).
VESA A was a good idea and an excellent effort but it was not flexible enough to survive, and it was very inefficient with regards to CPU usage.
  More results at FactBites »

 
 

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